TABLE OF CONTENTS xvii 



PACE 



The Causes of Mutations 340 



Mutation and Evolution. T. H. Morgan 341 



Chapter XXVII. Guiding Factors. Introduction .... 344 



Preliminary Discussion 344 



Adaptations 344 



Orthogenetic Trends 345 



Progressive Evolution . 345 



Specialization 346 



Increase in Size 348 



Increase in Intelligence 348 



Chapter XXVIII. Adaptation in Nature 349 



The Nature of Adaptations 340 



Two Categories of Adaptations 353 



Adaptations Classified 354 



Some Special Adaptations 355 



Parasitism and Degeneration 356 



Adaptations of Deep-Sea Animals and of Cave Animals . . .35c; 



Color and Pattern in Animals 360 



Osborn's Laws of Adaptation 366 



Chapter XXIX. The Web of Life. J. Arthur Thomson . . . 370 



Chapter XXX. Natural Selection 383 



Summary of Darwin's Natural-Selection Theory. Vernon L. Kellogg 383 



Objections to Selection 385 



Defense of Selection 390 



General Defense of Selection. J . L. Tayler 391 



Experimental Support of the Effectiveness of Natural Selection . 394 



The Present Status of Natural Selection 396 



The Relation of Mendelism and the Mutation Theory to Natural 



Selection. C. C. Nutting 396 



Chapter XXXI. Are Acquired Characters (Modifications) 



Hereditary? 401 



Misunderstandings as to the Question at Issue. /. Arthur Thomson 401 

 The Inheritance or Non-Inheritance of Acquired Characters. Edwin 



Grant Conklin 408 



The Other Side of the Question 414 



A Possible Mechanism for the Transmission of Acquired Characters. 



Michael F. Guyer 416 



Recent Experiments Believed to Favor the Lamarckian Theory . 423 



Chapter XXXII. Other Possible Guiding Factors .... 426 



Orthogenesis 426 



Vitalistic Theories 428 



